This invention relates to osteogenic devices, and more specifically to synthetic implants which induce osteogenesis in vivo. More particularly, this invention relates to biocompatible, bioresorbable, synthetic matrices which promote endochondral bone growth in vivo.
The potential utility of an osteogenic device capable of inducing endochondral bone formation in vivo has been recognized widely. It is contemplated that the availability of such a device would revolutionize orthopedic medicine, certain types of plastic surgery, and various periodontal and craniofacial reconstructive procedures.
The developmental cascade of bone differentiation in mammalian bone tissue is well documented in the art (Reddi (1981) Collagen Rel. Res. 1:209-226). Though the precise mechanisms underlying the phenotypic transformations are unclear, it has been shown that the natural endochondral bone differentiation activity of bone matrix can be dissociatively extracted and reconstituted with inactive residual collagenous matrix to restore full bone inducing activity (Sampath et al. (1981), Proc. Natl. Acad. Sci. USA 78:7599-7603).
Mammalian bone tissue is known to contain one or more active factor(s) which are proteinaceous materials capable of inducing the developmental cascade of cellular events resulting in endochondral bone formation. This active factor has variously been referred to in the literature as bone morphogenetic or morphogenic protein, bone inductive protein, osteogenic protein, osteogenin, or osteoinductive protein. Recently, the protein factors referred to as osteogenic protein (OP) responsible for inducing osteogenesis have been purified, expressed in recombinant host cells, and shown to be truly osteoinductive when appropriately sorbed onto a matrix. (U.S. patent application Ser. No. 179,406).
Studies have shown that while osteoinductive proteins are active cross species, the collagenous bone matrix heretofore required for inducing endochondral bone formation is species specific (Sampath and Reddi (1983) Proc. Natl. Acad. Sci. USA 80:6591-6594). Implants of demineralized, extracted xenogenic bone matrix and OP invariably have resulted in a strong inflammatory response that has inhibited osteogenesis, presumably due to immunogenic protein components in the bone matrix. Hence, osteoinduction requiring the use of allogenic bone matrix is a serious limitation with respect to human clinical use, as human bone is neither readily available nor cost effective.
The current state of the art of materials used in surgical procedures requiring conductive bone repair, such as the recontouring or filling in of osseous defects, is disclosed by Deatherage (J. Oral Maxillofac. Surg. (1988) 17:395-359). All of the known implant materials described (hydroxlapatite, freeze-dried bone, or autogenous bone grafts) have little or no osteoinductive properties. Clearly, the ability to induce osteogenesis is preferred over bone conduction for most procedures.
U.S. Pat. No. 4,795,467 discloses a bone repair composition comprising calcium phosphate minerals and a telopeptide, reconstituted, cross-linked fibrillocollagen. U.S. Pat. No. 4,563,350 discloses an osteogenic device comprising a bone-inducing extract and a collagenous matrix composed of approximately 90% trypsinized bovine bone matrix and 10% bovine dermal collagen. U.S. Pat. No. 4,789,663 discloses a method of effecting conductive bone repair comprising exposing the defect to fresh bone, and using xenogenic collagen from bone and/or skin, wherein the collagen is enzymatically treated to remove telopeptides, and is artificially cross-linked. EPO 309,241 discloses a device for inducing endochondral bone formation comprising an osteogenic extract, and a matrix carrier comprising 60-90% mineral component and 2-40% collagen. Deatherage et al., (Collagen Rel. Res. (1987) 7:2225-2231) purports to disclose an apparently xenogenic implantable device comprising a bovine bone matrix extract and Type 1 human skin collagen. Co-pending patent application Ser. No. 422,613, filed Oct. 17, 1989, entitled "Bone Collagen Matrix for Xenogenic Implants," discloses a xenogenic bone implant prepared from demineralized bovine bone and including osteogenic protein.
It is an object of this invention to provide a biocompatible, biodegradable bone matrix, implantable in a mammalian host with no significant inhibitory immunogenic response. Another object is to provide a matrix which is biocompatible, biodegradable, and which is capable of inducing osteogenesis when incorporated with osteogenic protein in mammals, including humans. Still another object is to promote conductive bone growth in mammals, including humans. Yet other objects are to provide a superior material for coating implantable prothetic devices, and to increase the cellular ingrowth into such devices. Yet another object of the invention is to provide a method for the production of such matrix material.
These and other objects and features of the invention will be apparent from the description, drawings, and claims that follow.